LATTICE MODEL FOR POLYMER PROPAGATION IN CONFINED MEDIA

Self-avoiding walks in 2-d and 3-d lattices are implemented as models of polymer propagation in confined media like vesicle bilayers and mic elles. Simulations conducted on such microreactors of various sizes (t otal number of monomers N(tot) between 80 and 10(6)) and shapes show t hat the propagation rate essentially depends on the ratio of the degre e of polymerization (D.P.) and N(tot). A scaling function is proposed giving excellent agreement with the simulations: it features a decreas e of the rate of propagation arising from a direct boundary effect, re lated to the contact between the radical and the impermeable boundarie s of the lattice, and from an exponential factor, accounting for the c onfinement effect. Taking into account this rate dependence on the D.P ., length and mass distributions are shown to be increasing functions of the D.P. when the rate of termination (by transfer) is small enough . In this limit, these distributions present a sharp increase in the v icinity of a D.P. about N(tot). This accumulation of polymers at a D.P . close to N(tot) entails a significant decrease of the polydispersity .